Phase contrast X-ray imaging, i.e. differential phase contrast imaging, is used, for example, to enhance contrast of low-absorbing specimen in comparison to conventional attenuation contrast images. EP 1 731 099 A1, also published as U.S. Pat. No. 7,889,838 B2, describes an X-ray interferometer arrangement comprising a polychromatic X-ray source, a source-grating, a phase-grating, and an analyzer-grating in addition to an image detector. An object is arranged between the source-grating and the phase-grating. The gratings comprise a plurality of X-ray transparent slits between bars of absorbing material, for example gold. However, the X-ray interferometer arrangement is providing phase contrast information in only one direction.